Exemplary embodiments of the present invention relate to a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants and a method for operation of the device.
Repairing structural components made from fibre-reinforced plastic (FRP) by gluing joints is problematic because of the possible presence of contaminations in the plastic, which may considerably impair the bond strength of the glued joint. If, in operation, an FRP component is exposed to environmental conditions with liquid or gaseous substances which can diffuse into the plastic, this may massively impair the adhesion point and possibly result in a total failure of the adhesive joint. For this reason the adhesive bonding repair of FRP components was previously prohibited in civil aviation.
It is possible, by means of sensors such as metal oxide sensors (MOX sensors), non-dispersive infrared sensors (NDIR sensors) and/or humidity sensors to detect or even to measure the contaminants in question. This represents a very considerable expenditure only because each contaminant requires discrete sensors or sensor settings and therefore the examination for the presence of several possible contaminants is very costly both structurally and in terms of process engineering.
Exemplary embodiments of the present invention are directed to a structurally simple device that can be used in a simple and error-resistant manner by means of which a FRP component can be examined for the presence of a plurality of specific contaminants.
According to a first aspect of the invention a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants, wherein in a mobile integral unit this device comprises the following: a surface heating device for regional heating of a part-zone of the fibre-composite component to be bonded for the purpose of desorption of contaminants; a sensor array with a plurality of sensors for detection of all contaminants in the gas phase; a control device for regulating the surface heating device and also for activation and for readout of the sensor array and also for ascertaining and signalling contaminations which are found.
By the direct heating of a region of the surface to be treated either by means of heat conduction or heat radiation the construction according to the invention enables thermal desorption of contaminants, wherein solid or liquid phases are directly converted into the gas phase. For this purpose it is necessary for the temperature to be monitored during the process of heating of the component, to avoid unacceptably high temperatures that could damage the component. The sensor array has a sufficiently large number of sensors by which all contaminants to be to detected can be detected simultaneously, so that the testing process can be kept brief. If one or more contaminants are ascertained, a corresponding signal is optically and/or acoustically output to the user. A binary testing for the contaminants (present in critical concentration, not present) or a more precise measurement of the detected concentration can be provided, but this increases the required apparatus. An advantage of this is that it is possible to operate without a transport or carrier gas, and so the gas concentration remains undiluted, resulting in an increase in the sensitivity and the sensor speed. Furthermore the walls can be kept easily accessible for collection of the contaminants and thus cleaning and restarting the sensor can be simplified.
According to an advantageous modification of this embodiment of the invention the surface heating device is constructed as a contact heating device. In this case a heated punch is preferably provided, which is heated internally and has a sufficient thermal mass or thermal capacity, in order to effect the lowest possible temperature fluctuations during the process of heating the structural component. However, this design has the disadvantage that heating or measuring is only possible on accessible and level areas of the FRP structural component.
A modification provides that the heated punch is disposed centrally and is surrounded by the sensor array, which in turn is surrounded by an outer housing. In this way a very compact design is possible with good detection of the desorbed substances.
According to an alternative embodiment the device comprises a central heated punch that is surrounded by an annular scattered light chamber with reflecting walls, and also at least one IR light emitter is provided that radiates into the scattered light chamber and several selective photodetectors are disposed in the wall of the scattered light chamber. Both designs can also be combined, that is to say that further MOX sensors can be disposed in the scattered light chamber in addition to the NDIR sensors.
According to another modification the surface heating device is constructed as a heat radiating device. It is particularly preferable to use a halogen lamp, which can be used with lenses and mirrors for targeted irradiation of surface regions of almost any shape. In this case the temperature of the irradiated surface is measured directly, preferably by means of a radiation thermometer, wherein the radiant heat generation can be adjustable by suitable control devices as a function of the recorded temperature.
In a preferred modification of the invention the heat radiating device is disposed centrally and the sensor array is disposed around the radiation range, and an optical thermometer coupled to a control device is provided for measuring the temperature of the irradiated part-region. This structurally compact arrangement ensures that the desorbed substances remain in the detection region and can be reliably detected.
In a preferred modification of the invention the surface heating device and the sensor array can be disposed on different sides of the fibre-composite component. This embodiment has the advantage that contaminants are “pushed out” by the heat, i.e. diffuse in the matrix in a substantial part against the temperature gradients.
According to a second aspect of the invention a device for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants, includes an extractor device for extraction of machining dust from the fibre-composite component; a filter device for collecting the machining dust particles a desorption device for thermal desorption of contaminants out of the dust particles; a sensor array with a plurality of sensors for detection of all contaminants in the gas phase; a control device for regulating the desorption device, activation and for readout of the sensor array, and ascertaining and signalling of contaminations that are found.
In this embodiment there is no heating of the structural component itself, so that a thermal damage thereto can be ruled out. Instead, the milling or grinding process which is necessary before an adhesive joint is utilised in order to analyse the removed material. This construction has the advantage that a substantially larger quantity of contaminants can be desorbed by the massively enlarged surface, so that a substantially more precise detection of the contaminants is possible. Also there is no need to adhere to thermal limiting values of the structural component, it is only necessary to ensure that no thermal decomposition processes of the plastic occur that can falsify the measurement results. A disadvantage of this construction is the substantial cost of apparatus, because the machining dust must be extracted, collected and then delivered to a desorption device.
According to an advantageous modification of both aspects of the invention the sensor array comprises a number of metal oxide gas detectors (MOX), which are each sensitive for individual contaminants. These sensors are structurally simple and can be adapted to different substances to be detected.
According to an advantageous modification of both aspects of the invention the sensor array comprises at least one humidity sensor. Since the moisture content of a FRP component influences the adhesion of a bond, a high moisture content is just as harmful as contamination by special substances.
According to an advantageous modification of both aspects of the invention the sensor array comprises at least one non-dispersive infrared sensor (NDIR). A plurality of infrared sensors are preferably provided which are selective for specific frequency ranges, and of which the selectivities are adapted to the substances to be detected.
According to an advantageous modification the individual sensors of the sensor array are selective for one or more of the following contaminants (usual English names or trade names used in the aviation industry in brackets):
surfactants (aircraft surface cleaner)
synthetic esters (jet oil 2)
alcohols, glycols and mixtures thereof (runway deicer)
alcohols (developer U89)
petrol, kerosene
butyl phosphates, phenyl phosphates, phosphate esters (hydraulic fluids, z.B. Skydrol)
mineral oils (turbine oil 500)
potassium acetates, sodium formiates (Clariant safeway)
phosphates, silicates (wet cleaner Surtec 121)
water, moisture
butanones, methyl ethyl ketone (MEK solvent)
hydrocarbons, silicones, fluorocarbons (release agent)
synthetic oils and lubricants.
According to an advantageous modification of the invention the composite component is an aircraft component. Thus, by the use of the device according to the invention, composite components in aircraft can be tested for the presence of contaminants and can optionally be repaired by bonding, which hitherto has not been allowable.
A method for testing a fibre-composite component, which is to be processed by means of bonding, for the presence of at least one substance out of a selection of possible contaminants provides for the use of the device described herein for performing an analysis of the machining dust. Thus in the grinding process for preparation of the adhesive surface the machining dust can preferably be collected and then analysed. If no contaminants are revealed, a subsequent surface analysis can either be omitted completely or can be carried out in simplified form. On the other hand, if contaminants are ascertained, a precise analysis of the substances is carried out by means of the device described herein.